Photoelectric Dye May Restore Some Sight to the Blind

BioPhotonicsJun 2015
OKAYAMA, Japan — Photoelectric dyes may be used to send images to the brains of the blind, potentially presenting a simpler alternative to artificial eyes based on image sensors.

Blind patients with hereditary diseases such as retinitis pigmentosa have dead photoreceptor cells, but other neurons involved in sight remain alive and can be stimulated artificially.

Researchers from Okayama University and Okayama University of Science tested the dye in genetically blind rats and found they were able to follow the direction of movement of a spinning drum painted with vertical black and white stripes.

The researchers rotated a drum with black-and-white vertical stripes either clockwise or counterclockwise at 2 or 4 revolutions per minute around rats with retinal implants. Instances when the rats turned their heads in the same direction as the rotation of the drum were counted as indications that the rat had recovered some level of sight. Courtesy of Okayama University.
The dye used has an absorption spectrum that spans the visible range from 400 to 600 nm. It is also stable, readily synthesized and has a low molecular weight and no obvious toxic components, the researchers said.

Coupled to a soft thin polyethylene film at a concentration of around 106 dye molecules per square micron, the dye was inserted into the subretinal area through a small opening so that a large film could be fitted, providing a large field of view.

Polyethylene has been used for medical implants for some time and its safety and stability has already been proved, the researchers said. They tested the toxicity of the dye in vitro using cultured retinal cells and observed no cytotoxicity.

“The prototype of the photoelectric dye-coupled retinal prosthesis, OUReP, is unique in using electric potentials to stimulate retinal neurons, in contrast with the other systems of retinal prostheses that generate electric currents,” the researchers said.

Next the researcher plan to test the likelihood of treatment success by using optical coherence tomography to assess the level of degeneration in the patient retinas.